1. Field of the Invention
The present invention relates in a general way to the quality check of a digital transmission link in the presence of real traffic. More particularly, the invention relates to quality check equipments complying with the CCITT recommendations on this matter, indicating transmission errors at bit level and in which the error detection preferably uses a cyclic redundancy coding (CRC).
2. State of the Prior Art
The gradual implementation of the integrated services digital telecommunications networks such as French ISDN network "NUMERIS" and the advent of the associated digital services point to increased demand from users with regard to quality in the forthcoming years. All-digital systems theoretically authorize precise quantitative measurements of transmissions quality and it is desirable to do away with all quality criteria of a subjective type in both data transmission and voice transmission.
In the recommendation G-821, Geneva 1980, pages 30 to 40 the CCITT International Telegraph and Telephone Consultative defined quality parameters for digital sections, links and paths throughout a network with or without switching exchanges. The measurement of these quality parameters currently requires the link in question being temporarily turned off and the injection into the link of a pseudorandom digital sequence of which the composition is known in advance. A comparison between the transmitted sequence and the received sequence enables rigourous bit-level detection of the transmission errors, and the quality parameters according to the CCITT recommendation are then calculated.
In the state of the art, there is no equipment available for measuring the CCITT quality parameters in a link in the presence of real traffic. Moreover, the errors detected by using cyclic redundancy codes generally concern a set of channels carried by the checked link and these errors cannot be specifically attributed to said channels.